CN105637620B - Nitride-based semiconductor - Google Patents

Abstract

The nitride semiconductor includes: an initial growth layer (2) formed on a substrate (1); a buffer layer (3) formed on the above initial growth layer (2); a supercrystalline layer formed on the above buffer layer (3) A lattice buffer layer (4); a channel layer (5) formed of multiple layers formed on the above-mentioned superlattice buffer layer (4); and a barrier layer (8) formed on the above-mentioned channel layer (5), The above-mentioned superlattice buffer layer (4) is alternately laminated by Al _x Ga _1-x N (0.5 ≤ x ≤ 1.0) composition of high Al-containing layer of thickness a and Al _y Ga _1-y N (0 ≤ y≤0.3) composed of a low Al-containing layer of thickness b, the above-mentioned channel layer (5) is joined to the above-mentioned superlattice buffer layer (4), and passes through from the superlattice buffer layer (4) side Al _z Ga _1-z N layer (6) and GaN layer (7) are stacked in order to form, the Al composition of above-mentioned Al _z Ga _1-z layer (6) and the average Al of above-mentioned superlattice buffer layer (4) The composition is the same.

Description

Nitride semiconductor

technical field

The present invention relates to nitride semiconductors. Specifically, it relates to the structure of a channel layer for improving the lifetime of a nitride semiconductor device.

Background technique

As an electronic device using a nitride semiconductor, a structure using a heterojunction composed of AlGaN and GaN is generally employed.

The specific structure is as follows, including: a buffer layer composed of nitride semiconductor formed on a substrate such as sapphire or Si; a channel layer generally composed of GaN formed on the above buffer layer; a channel layer formed on the above GaN channel layer A barrier layer made of AlGaN; a source and a drain forming ohmic contact with the two-dimensional electron gas region formed at the interface of the AlGaN barrier layer and the GaN channel layer; formed between the source and the drain between the gates.

In the case of forming a nitride semiconductor on a sapphire substrate or a SiC substrate, although there is no major problem, in the case of using a Si substrate with a smaller thermal expansion coefficient than a nitride semiconductor, the growth of the nitride semiconductor layer is backward. The downward bending becomes a convex shape, and the crystal itself forms cracks due to stress. Therefore, it is not suitable for the formation of electronic devices.

As a method for alleviating the difference in thermal expansion coefficient between the Si substrate and the nitride semiconductor, there is "semiconductor electronic device" disclosed in JP-A-2005-85852 (Patent Document 1). In this semiconductor electronic device, a buffer layer, a GaN electron transfer layer (500nm), an AlGaN electron supply layer (20nm), and a GaN contact layer are sequentially stacked on a GaN insertion layer formed on a silicon substrate. Here, the above-mentioned buffer layer is composed of a single-layer or multi-layer first layer made of GaN and a single-layer or multi-layer second layer made of AlGaN in this order. In this way, by inserting the first layer and the second layer of different materials as the buffer layer, the direction of the dislocation defect propagating from the lower side is bent to suppress propagation in the growth direction.

However, the semiconductor electronic device disclosed in Patent Document 1 of the above-mentioned prior art has the following problems.

Here, FIG. 6 shows a two-dimensional electron gas generation mechanism of a nitride semiconductor. In FIG. 6 , on the GaN layer (the GaN electron transport layer in the above-mentioned Patent Document 1) whose stress is relaxed and has a substantially overall lattice constant, a thin layer with a small lattice constant that does not cause stress relaxation is formed. AlGaN layer (AlGaN electron supply layer in Patent Document 1 mentioned above). In this case, the piezoelectric polarization Ppe occurs due to the difference in spontaneous polarization Psp between the GaN layer and the AlGaN layer and the in-plane deformation of the AlGaN layer on the GaN layer due to stress +σ. As a result, two-dimensional electron gas (2DEG: 2-dimensional electrons) is formed at the interface.

According to the same principle, as shown in FIG. 7, in the buffer layer (GaN(Al composition=0)/AlGaN(1≥Al composition>0 ) buffer layer) as an average block, it can be considered equivalent to a stress-relaxed AlGaN layer. Therefore, the GaN layer formed on the stress-relaxed AlGaN layer (the GaN electron transport layer in the aforementioned Patent Document 1) has a larger lattice constant than the AlGaN layer. While deforming, two-dimensional hole gas (2DHG: 2-dimensional hole gas) is formed at the interface.

In this way, the two-dimensional hole gas generated in the electronic device becomes a cause of leakage current, causing a problem in that device characteristics are degraded.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2005-85852

Contents of the invention

The technical problem to be solved by the invention

Therefore, the technical problem of the present invention is to provide a nitride semiconductor that suppresses the generation of two-dimensional hole gas when using a superlattice buffer layer formed by alternately and repeatedly stacking AlGaN layers of different compositions.

Technical solutions for problem solving

In order to solve the above problems, the nitride semiconductor of the present invention is characterized in that it includes:

Substrate;

an initial growth layer formed on the substrate;

a buffer layer formed on the initial growth layer;

a superlattice buffer layer formed on the buffer layer;

a channel layer composed of multiple layers formed on the above-mentioned superlattice buffer layer; and

a barrier layer formed on the above-mentioned channel layer,

The above-mentioned superlattice buffer layer is alternately laminated with Al _x Ga _{1 -y N} (0. ) is formed by forming a low Al-containing layer of thickness b,

The channel layer is joined to the superlattice buffer layer, and is formed by stacking at least an AlzGa1 _{-zN layer} and a GaN layer sequentially from the superlattice buffer layer side,

The Al composition of the above-mentioned AlzGa1 _{-zN layer} is the same as the average Al composition of the above-mentioned superlattice buffer layer.

In addition, in the nitride semiconductor according to one embodiment,

The Al composition _z in the above-mentioned AlzGa1 _-zN layer of the above-mentioned channel layer is determined by the following formula,

z=(a×x+b×y)/(a+b).

In addition, in the nitride semiconductor according to one embodiment,

The barrier layer above includes an _{AlwGa1 -wN} layer,

The Al composition w in the Al _w Ga _1-w N layer is a value larger than the Al composition z in the Al _z Ga _1-z N layer of the channel layer.

In addition, in the nitride semiconductor according to one embodiment,

The thickness a of the high Al-containing layer in the superlattice buffer layer is in the range of 1nm≤a≤5nm, and the thickness b of the low Al-containing layer is in the range of 22nm≤b≤30nm.

Invention effect

As can be seen from the above description, in the nitride semiconductor of the present invention, the channel layer joined to the AlGaN superlattice buffer layer is formed by laminating an AlzGa1 _{-zN layer} and a GaN layer in this order from the AlGaN superlattice buffer layer side. , and make the Al composition of the above-mentioned Al _z Ga _{1- z} N layer the same as the average Al composition of the above-mentioned AlGaN superlattice buffer layer. Therefore, the lattice constant of the above-mentioned AlzGa1 _{-zN layer} can be regarded as approximately equal to the lattice constant of the above-mentioned AlGaN superlattice buffer layer equivalent to one AlGaN layer in which stress is relaxed. Therefore, it is possible to suppress the formation of two-dimensional hole gas due to deformation caused by -σ stress at the interface between the AlGaN superlattice buffer layer and the Al _z Ga _1-z N layer.

Therefore, the two-dimensional hole gas formed between the superlattice buffer layer and the GaN layer is compensated by the AlzGa1 _{-zN layer} formed on the superlattice buffer layer, and the leakage current can be reduced. .

Description of drawings

FIG. 1 is a cross-sectional view of a nitride semiconductor epitaxial wafer as a nitride semiconductor according to the present invention.

FIG. 2 is a graph showing C-V measurement results of a HEMT (High Electron Mobility Transistor: High Electron Mobility Transistor) using the nitride semiconductor epitaxial wafer shown in FIG. 1 .

Fig. 3 is a diagram showing a C-V measurement method.

FIG. 4 is a cross-sectional view of a nitride semiconductor epitaxial wafer different from FIG. 1 .

FIG. 5 is a graph showing C-V measurement results of a HEMT using the nitride semiconductor epitaxial wafer shown in FIG. 4 .

Fig. 6 is a diagram showing the mechanism of two-dimensional electron gas generation.

Fig. 7 is a diagram showing the mechanism of two-dimensional cavitation gas generation.

Detailed ways

Hereinafter, the present invention will be described in detail using the illustrated embodiments.

· The first embodiment

FIG. 1 is a cross-sectional view of a nitride semiconductor epitaxial wafer that is the aforementioned nitride semiconductor according to the present embodiment. In FIG. 1 , an AlN initial growth layer 2 made of AlN with a thickness of 100 nm and an Al _0.2 Ga _0.8 N buffer layer 3 with a thickness of 20 nm are sequentially formed on a Si substrate 1 . Next, a superlattice buffer layer 4 was formed in which an AlN layer with a thickness of 4 nm and an Al _0.1 Ga _0.9 N layer with a thickness of 23 nm were laminated alternately and repeatedly at a cycle of 100 cycles.

Then, channel layer 5 composed of multiple layers is formed on superlattice buffer layer 4 . The channel layer 5 is formed by sequentially laminating an AlzGa1 _{-zN layer} 6 and a GaN channel region 7 as the GaN layer.

Here, in the superlattice buffer layer 4, a high Al-containing layer with a thickness of "a (nm)" formed of AlxGa1 _{- xN} (0.5≤x≤1.0) and _AlyGa In the case where the composition of _1-y N (0≤y≤0.3) forms a low Al-containing layer with a thickness of “b (nm)”, in the Al _z Ga _1-z N layer 6 of the above-mentioned channel layer 5 The Al composition z of is determined by the following formula (1).

z=(a×x+b×y)/(a+b)…(1)

Therefore, in this embodiment, the Al composition z of the Al _z Ga _1-z N layer 6 is z=(4×1+23×0.1)/(4+23)=0.23, and the thickness of the Al _0.23 Ga _0.77 N layer 6 is 1 μm growth.

Thereafter, a GaN channel region 7 was grown to a thickness of 20 nm on the above-mentioned Al _0.23 Ga _0.77 N layer 6 to form a channel layer 5 .

Here, it is desirable that the thickness "a" of the AlxGa1 _{- xN} layer (0.5≤x≤1.0) as the above-mentioned high Al-containing layer in the above-mentioned superlattice buffer layer 4 is 1nm≤a≤5nm, as the above-mentioned low The thickness "b" of the _{AlyGa1 -yN} layer (0≤y≤0.3) containing the Al layer is 22nm≤b≤30nm. The reason for this is as follows.

That is, in the case where the superlattice buffer layer 4 is formed by repeatedly laminating the above-mentioned AlxGa1 _{-xN layer as a high Al-containing layer and the AlyGa1- yN layer as} a low Al-containing layer, in order to effectively To suppress warping of the obtained nitride semiconductor epitaxial wafer, the difference between the thickness "a" of the high Al-containing layer and the thickness "b" of the low Al-containing layer needs to be at least 17 nm or more. Furthermore, it is necessary to make the thickness "a" of the easily bendable high-Al-containing layer thinner than the thickness "b" of the difficult-bend low-Al-containing layer. In this case, when the thickness "a" of the high Al-containing layer is less than 1 nm, the superlattice buffer layer 4 has a structure close to the same as the case where the low Al-containing layer is a single-layer film, and warpage cannot be effectively suppressed. In addition, when the thickness "b" of the low-Al-containing layer exceeds 30 nm, the superlattice buffer layer 4 has a structure close to the same as that of the single-layer film of the low-Al-containing layer, and warpage cannot be effectively suppressed. Therefore, it is effective to set the thickness "a" of the high Al-containing layer and the thickness "b" of the low Al-containing layer within the above ranges.

After this, an AlGaN barrier layer 8 of Al _0.4 Ga _0.6 N was formed with a thickness of 15 nm on the GaN channel region 7 of the channel layer 5 . Here, it is desirable that the Al composition “w” of the Al _w Ga _1-w N barrier layer 8 is larger than the Al composition “z” of the Al _z Ga _1-z N layer 6 of the channel layer 5 . The reason for this is as follows.

That is, when _{a HEMT} (High ElectronMobility Transistor: High Electron Mobility Transistor) is formed using the nitride semiconductor epitaxial wafer obtained in this embodiment, as shown in FIG. The interface of the GaN channel region 7 is deformed by stress +σ, and it is necessary to form a two-dimensional electron gas at the interface. In this case, since the GaN channel region 7 is _stacked on the _{AlzGa1 -zN layer} 6, as shown in _FIG . Deformation caused by stress - σ. Therefore, the interface between the _{AlwGa1 -wN} barrier layer 8 and the GaN channel region 7 needs to be deformed more than the interface between the GaN channel region 7 and the AlzGa1 _{-zN layer} 6 . Therefore, the Al composition "w" of the Al _w Ga _1-w N barrier layer 8 needs to be larger than the Al composition "z" of the Al _z Ga _1-z N layer 6 of the channel layer 5 .

In some cases, an AlN intermediate layer (not shown) made of AlN may be grown between the GaN channel region 7 and the AlGaN barrier layer 8 in order to improve mobility. In addition, a GaN cladding layer (not shown) made of GaN may be grown on the AlGaN barrier layer 8 .

In this way, it is possible to obtain a nitride semiconductor epitaxial wafer in which AlxGa1 _{- xN} (0.5≤x≤1.0) high-Al-containing layers having a thickness a and _AlyGa1 layers having _a thickness b are alternately stacked _-y N (0≤y≤0.3) AlGaN superlattice buffer layer 4 formed by a low-Al content layer is formed with an Al _z Ga _1-z N layer 6 and a GaN trench whose Al composition is determined by the above formula (1) In other words, a nitride semiconductor in which an AlGaN layer 6 having the same Al composition as the average Al composition of the superlattice is formed on the AlGaN superlattice buffer layer 4 can be obtained. Epiwafer.

In addition, in this embodiment, the combination of the AlGaN layer 6 and the GaN channel region 7 is used as the above-mentioned channel layer 5 , but it is not limited to this combination.

FIG. 2 shows the results of C-V measurement (capacitance measurement) in the above HEMT formed using the obtained nitride semiconductor epitaxial wafer. Of these, FIG. 2( a ) shows the case of this embodiment in which a combination of a GaN channel region 7 and an AlGaN layer 6 is used as the channel layer 5 . In addition, FIG. 2( b ) is a case of a comparative example using only a GaN layer as a channel layer. In addition, the horizontal axis "au" in the figure represents the relative distance to the substrate direction based on the surface of the above-mentioned wafer.

Here, in the above-mentioned C-V measurement, as shown in FIG. 3 , a bias voltage is applied between the gate G of the HEMT 10 and the submount 11 by the LCR measuring device 12 .

It can be seen from FIG. 2( b ) that when only GaN is used as the channel layer, a carrier concentration peak 13 can be seen between the GaN layer and the superlattice layer, implying the presence of two-dimensional hole gas. On the other hand, in the case of FIG. 2(a) in which the AlGaN layer 6 having the same Al composition as the average Al composition of the superlattice is formed on the superlattice buffer layer 4, no two-dimensional hole gas is generated. The peak of the induced carriers indicates that the generation of two-dimensional hole gas is suppressed.

As described above, according to the nitride semiconductor epitaxial wafer of this embodiment, the AlGaN layer having the same Al composition as the average Al composition of the superlattice is formed between the AlGaN superlattice buffer layer 4 and the GaN channel region 7 . Layer 6.

In this case, it can be considered that the AlGaN superlattice buffer layer 4 in which AlGaN layers having different Al compositions are alternately grown is equivalent to one AlGaN layer whose stress has been relaxed. Furthermore, the AlGaN layer 6 formed on the one stress-relaxed AlGaN layer has the same Al composition as the average Al composition of the superlattice buffer layer 4 equivalent to the above-mentioned one stress-relaxed AlGaN layer. It is considered that the lattice constant is approximately equal to that of the superlattice buffer layer 4 . Therefore, it is possible to suppress the formation of two-dimensional hole gas due to deformation caused by stress −σ at the interface between the superlattice buffer layer 4 and the AlGaN layer 6 .

Therefore, the AlGaN layer 6 formed on the superlattice buffer layer 4 compensates for the two-dimensional hole gas formed between the superlattice buffer layer 4 and the GaN layer, thereby reducing leakage current.

·Second Embodiment

FIG. 4 is a cross-sectional view of a nitride semiconductor epitaxial wafer as the nitride semiconductor of the present embodiment. In FIG. 4 , an AlN initial growth layer 22 made of AlN with a thickness of 100 nm and an Al _0.2 Ga _0.8 N buffer layer 23 with a thickness of 20 nm are sequentially formed on a Si substrate 21 . Next, a superlattice buffer layer 24 was formed in which AlN layers with a thickness of 3 nm and Al _0.1 Ga _0.9 N layers with a thickness of 25 nm were laminated alternately and repeatedly at a cycle of 100 cycles.

Next, the channel layer 25 composed of multiple layers is formed on the above-mentioned superlattice buffer layer 24 . The channel layer 25 is formed by laminating an AlzGa1 _{-zN layer} 26, an AlGaN layer 27 with a gradient Al composition, and a GaN channel region 28 as the GaN layer in this order.

Here, in the superlattice buffer layer 24, a high Al-containing layer having a thickness "a (nm)" formed of a composition of Al _x Ga _1-x N (0.5≤x≤1.0) and a layer of Al _y Ga _{1 -y} N (0 ≤ y ≤ 0.3) in the case of forming a low Al-containing layer with a thickness of "b (nm)", Al in the Al _z Ga _1-z N layer 26 of the above-mentioned channel layer 25 The composition z is determined by the above formula (1).

Therefore, in the present embodiment, the Al composition z of the Al _z Ga _1-z N layer 26 is:

z=(3×1+25×0.1)/(3+25)=0.20

The Al _0.2 Ga _0.8 N layer 26 is grown to a thickness of 1 μm.

Thereafter, on the above-mentioned Al _0.2 Ga _0.8 N layer 26, the Al composition is inclined from 0.2 to 0 in order from the Si substrate 21 side (inclined distribution), and an Al composition-inclined AlGaN layer 27 with a thickness of 100 nm is grown, and further, the GaN The channel region 28 is grown to a thickness of 20 nm to form the channel layer 25 .

Here, in the present embodiment, the thickness "a" of the AlxGa1 _{- xN} (0.5≤x≤1.0) high Al-containing layer in the superlattice buffer layer 24 is 1nm≤a≤5nm, The thickness "b" of the above-mentioned low Al-containing layer, that is, _{AlyGa1 -yN} (0≤y≤0.3) is 22nm≤b≤30nm. Therefore, making the difference between the thickness "a" of the high Al-containing layer and the thickness "b" of the low Al-containing layer at least 17 nm can effectively suppress warping of the obtained nitride semiconductor epitaxial wafer.

After this, an AlGaN barrier layer 29 of Al _0.4 Ga _0.6 N was grown to a thickness of 15 nm on the GaN channel region 28 of the above-mentioned channel layer 25 .

In some cases, an AlN intermediate layer (not shown) made of AlN may be grown between the GaN channel region 28 and the AlGaN barrier layer 29 in order to improve mobility. In addition, a GaN cladding layer (not shown) made of GaN may be formed on the AlGaN barrier layer 29 .

In this way, it is possible to obtain a nitride semiconductor epitaxial wafer as follows: an Al _x Ga _1-x N (0.5≤x≤1.0) high Al-containing layer with a thickness a and an Aly Ga _{1-y layer} with a thickness b On the AlGaN superlattice buffer layer 24 formed by alternate lamination of N (0≤y≤0.3) low-Al-containing layers, there are formed AlGaN layers 26 whose Al composition is determined by the above formula (1) and AlGaN layers 27 with Al composition gradients grown sequentially. The channel layer 25 formed of the GaN channel region 28, in other words, a nitride in which the AlGaN layer 26 having the same Al composition as the average Al composition of the superlattice is formed on the AlGaN superlattice buffer layer 24 can be obtained. Semiconductor epitaxial wafers.

In addition, in this embodiment, a combination of the AlGaN layer 26 , the Al composition gradient AlGaN layer 27 and the GaN channel region 28 is used as the channel layer 25 , but the combination is not limited to this.

FIG. 5 shows the above-mentioned C-V measurement results in the above-mentioned HEMT formed using the obtained nitride semiconductor epitaxial wafer. Of these, FIG. 5( a ) shows the case of this embodiment in which a combination of a GaN channel region 28 , an Al composition gradient AlGaN layer 27 , and an AlGaN layer 26 is used as the channel layer 25 . In addition, FIG. 5( b ) is a case of a comparative example using only a GaN layer as a channel layer.

Here, the above-mentioned C-V measurement method is the same as that of the above-mentioned first embodiment ( FIG. 3 ).

As can be seen from FIG. 5( b ), when only GaN is used as the channel layer, a carrier concentration peak 30 is seen between the GaN layer and the superlattice layer, suggesting the presence of two-dimensional hole gas. On the other hand, in the case of FIG. 5(a) in which the AlGaN layer 26 having the same Al composition as the average Al composition of the superlattice is formed on the superlattice buffer layer 24, no two-dimensional hole gas is generated. The peak of the induced carriers, indicating the suppression of two-dimensional hole gas generation.

As described above, in the nitride semiconductor epitaxial wafer of the present embodiment, the AlzGa1 _-zN layer having the same Al composition _z as the average Al composition of the superlattice is formed on the AlGaN superlattice buffer layer 24. 26. Therefore, as in the case of the above-mentioned first embodiment, the two-dimensional hole gas formed between the superlattice buffer layer 24 and the GaN layer is compensated by the AlGaN layer 26 formed on the superlattice buffer layer 24. , can reduce the leakage current.

Furthermore, in the present embodiment, as the above-mentioned channel layer 25 , an Al composition gradient AlGaN layer 27 is formed between the AlGaN layer 26 and the GaN channel region 28 . Since two-dimensional electron gas is generated in the channel layer 25, as shown in FIG. GaN layer (GaN channel region 28 ) with a lattice constant of volume. In this case, the GaN channel region 28 is stacked on the AlGaN layer 26 to form a structure capable of forming two-dimensional hole gas as shown in FIG. 7 .

Therefore, between the above-mentioned AlzGa1 _{-zN layer} 26 and the GaN channel region 28, an Al composition gradient AlGaN layer in which the Al composition is inclined from z to 0 in order from the Si substrate 21 side (inclined distribution) is formed. 27, thereby relieving the deformation generated in the GaN channel region 28, and suppressing the generation of two-dimensional hole gas at the interface.

Therefore, according to the present embodiment, the leakage current can be further reduced compared to the case of the first embodiment described above.

As described above, in the present embodiment, the strain generated in the GaN channel region 28 is alleviated by forming the Al composition gradient AlGaN layer 27 between the AlzGa1 _{-zN layer} 26 and the GaN channel region 28 . Therefore, larger deformation can be generated at the interface between the _{AlwGa1 -wN} barrier layer 29 and the GaN channel region 28 than at the interface between the GaN channel region 28 and the AlGaN layer 27 with an Al composition gradient, and two-dimensional electron gas can be generated.

However, it is preferable to make the Al composition "w" of the Al _w Ga _1-w N barrier layer 29 larger than the Al _z Ga ₁ in the channel layer 25 as in the case of the first embodiment above in terms of generating two-dimensional electron gas. _-z The Al composition of the N layer 26 is "z".

In addition, by slicing the nitride semiconductor epitaxial wafer according to each of the above-mentioned embodiments, a nitride semiconductor wafer as another example of the above-mentioned nitride semiconductor can be obtained.

As described above, the nitride semiconductor of the present invention is characterized by including:

Substrate 1, 21;

The initial growth layer 2, 22 formed on the above-mentioned substrate 1, 21;

buffer layers 3, 23 formed on the initial growth layers 2, 22;

superlattice buffer layers 4, 24 formed on the above buffer layers 3, 23;

Channel layers 5, 25 formed of multiple layers formed on the above-mentioned superlattice buffer layers 4, 24; and

The barrier layers 8, 29 formed on the above-mentioned channel layers 5, 25,

The above-mentioned superlattice buffer layers 4 and 24 are alternately laminated with Al _x Ga _1-y N (0.5 ≤ x ≤ 1.0) and Al _y Ga _1-y N (0 ≤ y≤0.3) formed by the low Al-containing layer of thickness b formed,

The channel layers 5, 25 are bonded to the superlattice buffer layers 4, 24, and at least AlzGa1 _{-zN layers} 6, 26 and GaN layers are stacked sequentially from the superlattice buffer layer 4, 24 side Layers 7, 28 are formed,

The Al composition of the AlzGa1 _{-z layer} 6, 26 is the same as the average Al composition of the superlattice buffer layer 4, 24 above.

It can be considered that the AlGaN superlattice buffer layers 4 and 24 are equivalent to a stress-relaxed AlGaN layer. Therefore, when the channel layers 5, 25 joined to the AlGaN superlattice buffer layers 4, 24 are formed of only the GaN layer, the GaN channel layer formed on the above-mentioned stress-relaxed AlGaN layer has a The constant is larger than that of the AlGaN layer, so it deforms on the tension side due to the stress -σ, and forms two-dimensional hole gas (2DHG) at the interface.

According to the above configuration, AlzGa1 _{-z layers} 6, 26 and GaN layers 7, 28 are sequentially stacked from the superlattice buffer layer 4, 24 side to form a channel layer joined to the superlattice buffer layer 4, 24 5, 25, and make the Al composition of the above-mentioned AlzGa1 _{-z layer} 6, 26 the same as the average Al composition of the AlGaN superlattice buffer layer 4, 24. Therefore, the above-mentioned AlzGa1 _{-z layers} 6, 26 can be regarded as having substantially the same lattice constant as the above-mentioned AlGaN superlattice buffer layers 4, 24 equivalent to one AlGaN layer whose stress has been relaxed. Therefore, it is possible to suppress the formation of two-dimensional hole gas due to deformation at the interface between the AlGaN superlattice buffer layers 4, 24 and the AlzGa1 _{-z layers} 6, 26 due to the stress -σ.

Therefore, the two layers formed between the above-mentioned superlattice buffer layer 4, 24 and the GaN layer 7, 28 are performed through the AlzGa1 _{-z layer} 6, 26 formed on the above-mentioned superlattice buffer layer 4, 24. Dimensional hole gas compensation can reduce leakage current.

In addition, in the nitride semiconductor according to one embodiment, the Al composition _z in the AlzGa1 _-z layer 6, 26 of the channel layer 5, 25 is determined by the following formula,

z=(a×x+b×y)/(a+b).

According to this embodiment, the Al composition _z of the above-mentioned AlzGa1 _-z layer 6, 26 in the above-mentioned channel layer 5, 25 is expressed by the formula "z=(a×x+b×y)/(a+b) "Decide. Therefore, the Al composition of the above-mentioned AlzGa1 _{-z layer} 6, 26 can be made the same as the average Al composition of the above-mentioned superlattice buffer layer 4, 24.

In addition, in the nitride semiconductor according to one embodiment, the barrier layer 8 includes an AlwGa1 _-wN layer 8, and the Al composition _w in the _{AlwGa1 - wN} layer 8 is lower than that of the channel layer 5. The Al composition in the above-mentioned Al _z Ga _1-z layer 6 has a large value of z.

When forming a HEMT using the obtained nitride semiconductor, it is necessary to deform the interface between the Al _w Ga _{1- w} N layer 8 of the barrier layer 8 and the GaN layer 7 of the channel layer 5 by stress +σ And a two-dimensional electron gas is formed at the above-mentioned interface. In this case, since the channel layer 5 is formed by laminating the GaN layer 7 on the _{AlzGa1 - z} layer 6, the stress _- σ resulting in deformation. Therefore, it is necessary to produce a larger gap at the interface between the _{AlwGa1 -wN} layer 8 of the barrier layer 8 and the GaN layer 7 of the channel layer 5 than the interface between the GaN layer 7 and the AlzGa1 _{-z layer} 6. deformation.

According to this embodiment, the Al composition w in the Al _w Ga _1-w N layer 8 is set to a larger value than the Al composition z in the Al _z Ga _1-z layer 6 of the channel layer 5 . Therefore, at the interface between the _{AlwGa1 -wN} layer 8 of the barrier layer 8 and the GaN layer 7 of the channel layer 5, the interface between the GaN layer 7 and the AlzGa1 _{-z layer} 6 can be produced. A large deformation can form a two-dimensional electron gas at the above-mentioned interface.

In addition, in the nitride semiconductor according to one embodiment, the thickness a of the high Al-containing layer in the superlattice buffer layers 4 and 24 is in the range of 1nm≤a≤5nm, and the thickness b of the low Al-containing layer is in the range of 22nm≤b≤30nm.

According to this embodiment, the difference between the thickness "a" of the above-mentioned high Al-containing layer and the thickness "b" of the above-mentioned low Al-containing layer in the above-mentioned AlGaN superlattice buffer layer 4, 24 is at least 17 nm or more, and the flexible The thickness "a" of the above-mentioned high-Al-containing layer is thinner than the thickness "b" of the above-mentioned low-Al-containing layer that is difficult to bend, so that dynamic bending of the obtained nitride semiconductor can be effectively suppressed.

Symbol Description

1, 21...Si substrate

2. 22...AlN initial growth layer

3. 23...AlGaN buffer layer

4. 24... superlattice buffer layer

5, 25... channel layer

6. 26...Al _z Ga _1-z N layer

7, 28...GaN channel region

8, 29... AlGaN barrier layer

10…HEMT

11…Abutment

12…LCD meter

13, 30...Peak carrier concentration

27... Al composition sloped AlGaN layer.

Claims (4)

1. a kind of nitride-based semiconductor, which is characterized in that including：

Substrate (1,21)；

The initial growth layer (2,22) being formed on the substrate (1,21)；

The buffer layer (3,23) being formed on the initial growth layer (2,22)；

The super-lattice buffer layer (4,24) being formed on the buffer layer (3,23)；

The channel layer (5,25) being made of multiple layers being formed on the super-lattice buffer layer (4,24)；With

The barrier layer (8,29) being formed on the channel layer (5,25),

The super-lattice buffer layer (4,24) passes through alternately laminated by Al_xGa_1-xN composition constitute thickness a high al-containing layers and By Al_yGa_1-yN composition constitute thickness b low al-containing layers and formed, wherein 0.5≤x≤1.0,0≤y≤0.3,

The channel layer (5,25), engages with the super-lattice buffer layer (4,24), and by from the super-lattice buffer layer (4,24) side, which is risen, is successively at least laminated Al_zGa_1-zN layers (6,26) and GaN layer (7,28) and formed,

The Al_zGa_1-zN layers (6,26) of Al composition is identical as the average Al composition of the super-lattice buffer layer (4,24),

The thickness a of the high al-containing layers is thinner than the thickness b of the low al-containing layers.

2. nitride-based semiconductor as described in claim 1, it is characterised in that：

The Al of the channel layer (5,25)_zGa_1-zAl composition z in N layers (6,26) is determined by the following formula：

Z=(a × x+b × y)/(a+b).

3. nitride-based semiconductor as claimed in claim 1 or 2, it is characterised in that：

The barrier layer (8) includes Al_wGa_1-wN layers,

The Al_wGa_1-wAl composition w in N layers (8) is than the Al of the channel layer (5)_zGa_1-zAl composition in N layers (6) Z big value.

4. nitride-based semiconductor as claimed in claim 1 or 2, it is characterised in that：

The range of the thickness a of the high al-containing layers in the super-lattice buffer layer (4,24) is 1nm≤a≤5nm, described low to contain The range of Al layers of thickness b is 22nm≤b≤30nm.